1. Field of the Invention
Embodiments of the present invention relate generally to inspection and testing of devices and more specifically to systems and methods to test integrity of solder joints or bumps used to attach integrated circuit chips, chip packages, and chip capacitors to PCBs and substrates.
2. Description of Related Art
Flip chip technology is a form of surface mount technology pioneered by IBM in early 1960s. This technology is generally where a bare die is flipped over and the active side of the die is then placed down on the substrate or lead frame using small conductive bumps made of solder or conductive adhesive. So far, the most common package interconnect is solder.
Solder bumps act not only as a mechanical connection, but also as an electrical interconnection between the die and substrate. The quality of solder joints is closely related to the reliability and performance of a flip chip device. A variety of solder joint defect types can be introduced during the manufacturing process of flip chip and other chips and chip packages that use solder, copper or other materials as a means of attachment to the substrate.
Common manufacture defects in solder joints include crack, head-in-pillow (HIP), open connection, shorted connection, starved solder joints, misaligned solder joints, missing solder bumps, and voids. Thermal cycling due to reflow, rework, and power cycles are also causes of cracked solder bumps that can appear during the life of the device.
Current trends, such as increasing I/O, decreasing pitch, decreasing diameter, vertical integration, and lead-free solder materials, will further intensify the focus on packaging research, with a special emphasis on quality and reliability. This places an ever-increasing importance on technologies that are capable of identifying solder joint defects in manufacturing and research applications to help reduce cost. Other new technologies (such as copper, etc.) for attaching devices to the substrate have been and are continuously being developed. Therefore even though solder bumps or joints are used herein to illustrate how devices are attached to various substrates, the present invention can also be used in these other device attachment methods.
Existing systems require a known good reference device to which inspected devices can be compared. Identifying known good reference devices via x-ray, electrical, or other contact inspection methods can be time consuming and expensive.
What is needed, therefore, are improved systems and methods enabling detection of defective solder bumps or joints that are efficient, reliable, and non-destructive. It is to the provision of such testing devices, systems, and methods that the various embodiments of the present invention are directed.